1. Field of the Invention
The present invention relates to a new and novel air flotation cell which can be used in a number of different services including concentration of mineral ores and waste water treatment such as oil removal from refinery waste waters and fiber recovery in the pulp and paper industry.
2. Description of the Prior Art
Commercially valuable minerals, for example, metal sulfides, apatitic phosphates and the like, are commonly found in nature mixed with relatively large quantities of gangue materials, and as a consequence it is usually necessary to beneficiate the ores in order to concentrate the mineral content thereof. Mixtures of finely divided mineral particles and finely divided gangue particles can be separated and a mineral concentrate obtained therefrom by well known froth flotation techniques. Broadly speaking, froth flotation involves conditioning an aqueous slurry or pulp of the mixture of mineral and gangue particles with one or more flotation reagents which will promote flotation of either the mineral or the gangue constituents of the pulp where the pulp is aerated. The conditioned pulp is aerated by introducing into the pulp a plurality of minute air bubbles which tend to become attached either to the mineral particles or to the gangue particles of the pulp, thereby causing these particles to rise to the surface of the body of pulp and form thereat a float fraction which overflows or is withdrawn from the flotation apparatus.
Typical of such flotation apparatus for accomplishing the foregoing is that disclosed in U.S. Pat. No. 3,371,779. In such apparatus, the conditioned pulp is introduced into a flotation compartment containing a relatively quiescent body of an aqueous pulp, and aerated water is introduced into the lower portion of the flotation compartment through orifices formed in the bottom wall of the flotation compartment. A body of aerated water is established in a hydraulic compartment disposed directly below the flotation compartment by introducing air and water into the hydraulic compartment while simultaneously dispersing a multitude of fine air bubbles throughout the water in the hydraulic compartment. The body of aerated water in the hydraulic compartment is in fluid communication with the aqueous pulp in the lower portion of the flotation compartment through the aforementioned orifices formed in the bottom wall of the flotation compartment. An overflow fraction containing floated particles of the pulp is withdrawn from the top of the body of aqueous pulp and an underflow or non-float fraction containing non-floated particles of the pulp is withdrawn from the pulp in the lower portion of the flotation compartment.
However, the device disclosed in the Hollingsworth et al U.S. Pat. No. 3,371,779 also has several disadvantages which were sought to be corrected by Hollingsworth in his subsequent patent, U.S. Pat. No. 4,287,054. Specifically, this latter patent is directed to the problems that there was no aeration immediately above the discharge pipe and that the coarser ore particles settled out on the constriction plate thereby inhibiting the passage of aerated water into the flotation cell.
To overcome the problem of no aeration immediately above the discharge pipe, U.S. Pat. No. 4,287,054 provides means for introducing air bubbles into the discharge pipe via orifices in the discharge pipe in communication with the hydraulic chamber or by employing an auxiliary aerating chamber above or below the discharge pipe. Other improvements shown in U.S. Pat. No. 4,287,054 include installing baffle plates attached to the constriction plates, and providing the bottom constriction plate with a slope either toward the central discharge pipe or the wall.
However, these flotation devices suffer from the disadvantage of having to use aspirators to form an intimate dispersion of fine bubbles throughout the water in the hydraulic chamber, and because aspirators do not permit the individual control of the air and water, such devices are difficult to operate. In addition, aspirators have a tendency to plug when unfiltered recycle water is used in the flotation devices.
Another problem with these devices is the possible plugging of the holes in the constriction plate in that they employ a large number of relatively small holes which are easily blocked.
Other examples of prior art relating to flotation are disclosed in, U.S. Pat. Nos. 1,192,228, 1,223,033, 3,012,670, 3,032,199, and 4,341,630.